i recently installed new valve covers on my car after i saw that my others had a small crack ( plastic junk ) after the install i started getting the ses light on and noticed that my car started to bog when the service engine light would flash on and off. now i have misfire codes when i diagnose the codes. i have replaced the battery, coil pacs, spark plugs, and fuel filter. i dont know where else to check. i took it to a local reputable shop and they dont know what it could be. if some one would please help me out it would be great